The progression of first meiotic prophase and synaptonemal complex (SC) formation in female rats, Rattus norvegicus S.D., is described through the analysis of the different stages of the first meiotic prophase, and confirms the high synchrony of the process in this species. Leptotene is a stage of very short duration and since pairing of the homologues begins very early, only a leptotene-zygotene stage can be distinguished. The progression of pairing during zygotene is asynchronous. The morphology of the SCs is similar to that described in other species. During diplotene and before desintegration of the lateral elements, desynapsis takes place. In some oocytes a double or even multiple nature of lateral elements was seen. Associations between SCs and nucleoli or nucleolar filaments are frequent. The presence of fragmented SCs can be interpreted as a technical artifact. © 1988 Kluwer Academic Publishers.